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Old 17th Sep 2019, 4:55 pm   #1
Draker4c
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Default Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

I know this subject has been touched on in other threads but could a knowledgeable forum member give pros and cons in use and in quality of build/ servicing issues between Stablilock and Marconi Radio Test Sets. I’m interested in frequencies up to 144 MHz only and would like to keep an eye on performance
my ancient Drakes, TS 930, and Racal receivers. Are components for such devices largely unobtanium. What would be the additional recommendations fo alternative devices.
Many thanks Hugh G1AUR
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Old 29th Oct 2019, 10:19 pm   #2
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

Hello forum
It’s been a little while re my above request for recommendations/ views on test sets. Could any esteemed members shed some light on this?
Many thanks
73 Hugh G1AUR
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Old 30th Oct 2019, 12:06 am   #3
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

In the period between your messages, I came across and bought a Schlumberger stabilock 4031, though I'd have been more at home with an HP8922.

The first thing to be aware of is these things were dedicated to testing stuff like PMR sets and have AM/FM modulators and demodulators. They can make and measure a continuous carrier, but don't do much for SSB sets. Later sets got hardware dedicated to analogue phones and then they evolved into mobile phone testers. Some kept AM/FM functionality well into the phone era.

Parts are mostly routinely available until you get to CPUs and the like. I soon found the manuals free on the internet.

These things are handy if you have to cart them around, but aren't as versatile as appropriate test gear like a sig gen, audio analyser, modulation meter, RF power meter, scope and spectrum analyser.

I got mine to leade it at the radio club, so there was at least some basic test gear there.

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Old 30th Oct 2019, 12:38 am   #4
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

Hello David
Many thanks for your reply and comments. As one of those interested parties who never attained a professional career in or experience of electronic design or maintenance I guess I was looking for a turnkey solution in a box but as you say SSB facilities or frequency coverage of HF amateur bands would not be foremost in test gear primarily aimed at PMR and mobiles. Even more of an excuse to stick to individual pieces of kit 😀 space and strength of workbench (or marriage) permitting !
73 Hugh G1AUR
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Old 30th Oct 2019, 6:35 am   #5
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

That Stabilock 4031 says it covers 0.4 to 1000 MHz, so HF is covered.

It has dual audio generators, so I think it might be possible to generate 2-tone audio for testing SSB transmitters.

An unmodulated carrier can do a lot for testing SSB/CW receivers.

So these one-box testers are still quite useful for HF amateur radio, but they don't do everything (they'd like you to think they did..)

In a conversation with Ian, G3ROO, a serial home-constructor if ever there was one, Ian said he wanted a spectrum analyser, but only needed one to cover the HF bands because he didn't bother with anything higher. I explained that one of the reasons for using an analyser was to check that a transmitter wasn't producing anything it shouldn't.

Now the HF bands stop at 29.7MHz, but there is no upper limit for the frequency range you don't want harmonics and spurii at. In general terms, coverage to 150MHz will check your first 5 harmonics and ought to be enough, but spurious oscillations in HF power amps can happen much higher. You really need an analyser that covers to 1GHz to tell if an HF transmitter is clean. Fortunately, such instruments are in the majority.

There's a nasty harmonic problem with aircraft VHF comms radios, the harmonics of some channels land right on the GPS frequencies, so unless you have a good radio, when you press PTT to talk, all your navigation gear loses its fix and can get seconds/minutes to get going again after you release the button. GPS signals are very weak due to limitations on satellite design back when the system was designed. So I have to do sensitive harmonic tests up round 1600MHz for the day-job.

I spent a while (about 30 years) designing RF test equipment at HP. Spectrum analysers, sig gens, etc. so the shack here is armed for bear in terms of test gear! So I know my way around the stuff, and like to pick up the odd instrument when I see something being sold non-working. If you can fix things, you can get some real bargains. However, the round tuit pile is quite something...

David
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Old 31st Oct 2019, 8:51 pm   #6
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

Thanks David
Any thoughts regarding quality of build, performance and general facilities of The Stabilock series (with and without crt) and the Marconi 2955 series?
73 Hugh G1AUR
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Old 31st Oct 2019, 9:32 pm   #7
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

Not a whole lot of thoughts, I'm afraid. I haven't used it in anger. Looking inside, I don't think the construction is quite up to the standard usually seen in later period Marconi products.

There are other testers like the HP8920A and 8922A which are fairly useful and very well built. R&S have also been active in the field.

I wasn't looking for a PMR tester, but I came across one and the price was within my spur of the moment purchase range. It just happened to be the Schlumberger. It's going to get donated to the local radio club who have a permanent clubhouse and are setting up a test/repair bench. It should give them a flying start.

My inclination at home is to have separate test gear. I'm not fixing things for hire or reward, so speed isn't an issue and I'd rather have the higher performance and unlimited versatility of general test gear. Oh, and when fixing stuff for others, my golden rule is that if they're not present and taking an interest, I'm doing something else! My aim is to teach them how to fix things and that is rather hard when they're not there. It also filters out those not really involved. I never make a charge, but it's amazing how those whose intent is to get something fixed for sale and profit vanish when some of their own time has to go into it. I think they divide the proft to be had by the time involved and discover a rather disappointing hourly rate.... it's a way of welcoming them to the real world

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Old 31st Oct 2019, 9:59 pm   #8
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

In times-past I was lucky enough to be able to support - for business-reasons (and so 100% tax-deductible) - a R&S Polyskop. Which was brilliant - when it worked (and when it didn't I happily paid someone else to fix it).

IMHO if you're dealing with HF SSB stuff you need something better than just a PMR-style AM/FM analyser - that won't really help you when it comes to setting the optimum carrier-frequencies for USB/LSB generation in a crystal-filter-based transceiver or aligning the bandpass-filters in a Racal triple-mix receiver.
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Old 31st Oct 2019, 10:00 pm   #9
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

Great pity you’re located in Fife and I Basildon David I would certainly be taking an interest in your advice and techniques. Now on the periphery of early retirement. I plan to gain as much knowledge and practical skills as I can simply out of the curiosity of processes and how stuff works ...may keep the little grey cells going for longer too! That’s my profit motive!
Many thanks for your responses.
73 Hugh G1AUR
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Old 31st Oct 2019, 10:43 pm   #10
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

G6Tanuki I totally agree with you. I have Drake TR7 and Trio TS 930SAT, Drake C Line and a a fair number of Racal receivers and adaptors. Probably not complex kit by the standards of many on the forum but certainly quite enough for me to get my head around! I guess there is a finite point in terms of my ability to troubleshoot, check and repair said kit in the future and I guess as a very recent forum member I’m getting the measure of what kit is out there to aid the process. I do fully appreciate that much may be done with very basic kit as the many of the posts here evidence . Certainly the right tool for the job is what I’m trying to quantify.
Thanks for you thoughts.
73 Hugh G1AUR
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Old 31st Oct 2019, 10:45 pm   #11
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

My vote also goes for separate test gear. The only real advantage of a test set is that it saves space on the bench. If the PSU, display, or processor system of your test set goes down, which is quite likely in older test gear, then your whole test bench goes down. With separate instruments it will only be one at a time!
Using (and repairing) individual instruments will also aid your understanding of how they work. The internal measurement and generator circuits inside a test set are often intertwined to save on hardware and unknitting them can be hard.
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Old 1st Nov 2019, 3:23 pm   #12
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Default Re: Recommendations for Test Set for HF Radio. Stabilock Marconi or something else.

All good points!

There is a trade off. Rather a lot of faults can be fixed with very basic test gear. That is often overlooked is that the level of knowledge needed to do this is often far from basic. There is a trade off between knowledge and amount of necessary gear which sets a boundary on what's possible.

A common mistake is to think that fancier bits of test gear are only needed as you get more advanced. This is actually the exact opposite. With a scope you can see and better envisage what is going on and pictures are great for helping understanding. If you stick to an AVO 8 you have to interpret the readings and try to imagine what is going on.

I encourage people to get a decent scope as it makes things clearer and easier to learn from. A good signal generator is also a great help.

Spectrum and network analysers may be pushing a bit too far for the typical home workshop, but if you come across one for a good price, pounce!

David
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